1. Field of the Invention
The present invention relates to a fault diagnosing apparatus for a vehicle and a fault diagnosing method for a vehicle.
2. Description of the Background Art
A vehicle, which has an electric motor generating the driving force, such as a hybrid vehicle, an electric vehicle and a fuel cell vehicle, incorporates a power supply system having a high voltage power supply. Here, a plurality of relays are provided between the high voltage power supply and an electric power converting circuit (inverter) for controlling connection and disconnection of the circuit.
In such a circuit, if the relays are connected when they actually should be released, the lifetime of the power supply may be reduced or devices connected to the circuit may be damaged due to a current from the high voltage power supply.
Accordingly, Japanese Patent Laying-Open No. 2004-303691 discloses a method for determining melting adhesion of relays in order to prevent such problems. According to the determining method, when melting adhesion is detected upon a melting adhesion check, a discharge process for discharging the stored charges in a smoothing capacitor is conducted and thereafter the melting adhesion check is again conducted, so that fault that is solved instantly is not detected.
Relays for connecting and disconnecting a high voltage battery and a high voltage system in a hybrid system have a mechanical drive mechanism employing an excitation coil. Thus, in some cases the system may not operate because of a temporary incidental factor such as dust clogging the drive unit. Such a failure is unlikely to be repeated, and may be solved easily by conducted on/off operations again.
Accordingly, even when melting adhesion of the relays is detected, the fault may not be confirmed on single detection, and on/off operations may be conducted again to thereafter conduct detection of melting adhesion again. In such a case, still a prolonged processing time for the fault determination is not preferable.
Repeating the discharge process as shown in Japanese Patent Laying-Open No. 2004-303691, the fault determination is delayed by the time required for charging and discharging the smoothing capacitor. An improvement may be made in order to notify the driver of the fault as soon as possible.